Ms Namba is one of the most outstanding entrepreneurs and executives in Japan, not least because she's a woman in one of the most misogynistic corporate cultures in the world, even though she shuns women's conferences and prefers to think about providing equal opportunity to all employees, rather than talk about gender.

DeNA bought Silicon Valley mobile gaming startup ngmoco for $400 million back in October. DeNA runs a mobile social gaming platform in Japan; think Zynga Mobile years before there was Zynga.

Last year the company generated over $1 billion in revenue and almost $400 million in profit, and has a market cap over $4 billion. Ms Namba left her job at McKinsey in 1999 to start DeNA.

She is abruptly stepping down as CEO to take care of her husband, who has a malignant tumor. She will remain on the company's board and keep an office to oversee international expansion. She said her husband supported her eschewing the traditional role of a Japanese woman and founding a company, so now it's her turn to support him.